Python浮动比率
问题描述
我尝试获取变量的比例并得到意想不到的结果.有人可以解释一下吗?
I try get ration of variable and get unexpected result. Can somebody explain this?
>>> value = 3.2
>>> ratios = value.as_integer_ratio()
>>> ratios
(3602879701896397, 1125899906842624)
>>> ratios[0] / ratios[1]
3.2
我使用 python 3.3
I using python 3.3
但我认为 (16, 5) 是更好的解决方案
But I think that (16, 5) is much better solution
以及为什么它适用于 2.5
>>> value = 2.5
>>> value.as_integer_ratio()
(5, 2)
解决方案
使用 fractions 模块 简化分数:
Use the fractions module to simplify fractions:
>>> from fractions import Fraction
>>> Fraction(3.2)
Fraction(3602879701896397, 1125899906842624)
>>> Fraction(3.2).limit_denominator()
Fraction(16, 5)
来自 Fraction.limit_denominator() 函数一个>:
From the Fraction.limit_denominator() function:
查找并返回与 self 最接近且分母最多为 max_denominator 的 Fraction.此方法对于找到给定浮点数的有理逼近很有用
Finds and returns the closest
Fractiontoselfthat has denominator at most max_denominator. This method is useful for finding rational approximations to a given floating-point number
浮点数精度有限，不能精确表示；你看到的是一个四舍五入的表示，但实数是:
Floating point numbers are limited in precision and cannot represent many numbers exactly; what you see is a rounded representation, but the real number is:
>>> format(3.2, '.50f')
'3.20000000000000017763568394002504646778106689453125'
因为浮点数表示为二进制小数的总和；1/5 只能通过将 1/8 + 1/16 + 1/128 + 更多的二进制分数相加来表示，以增加 2 的指数.
because a floating point number is represented as a sum of binary fractions; 1/5 can only be represented by adding up 1/8 + 1/16 + 1/128 + more binary fractions for increasing exponents of two.
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